The present invention relates to a flight control device for an aircraft, particularly a helicopter.
This device which may, in the context of the present invention, be a device of the mechanical or electrical flight controls type, comprises, in the known way, for control with respect to at least one control axis (roll, pitch, yaw):
at least one control (stick or mini-stick) which can be actuated by a pilot of the aircraft;
at least one actuating means (servocontrol) for actuating a controlled member (rotor) to which a command is applied; and
first means for determining and transmitting to the said actuating means a command that is dependent on a first value that represents the actuation of said control.
Although the invention may in principle be applied to any control axis (pitch, yaw, roll) of any type of aircraft, it is explained hereinbelow in greater detail with respect to the roll axis of a helicopter.
It is known that in forward flight, when the pilot of a helicopter actuates the roll control or stick, that is to say moves said stick sideways, the response of the helicopter to this command generally corresponds to an angular roll speed (or rate) which is more or less proportional to this movement. In the context of the present invention, this type of control will be known as xe2x80x9cspeed controlxe2x80x9d using a speed command (for example angular roll rate). Said speed command is appropriate to the performing of most conventional flying maneuvers.
In addition, the fact that the stick controls an angular roll rate, rather than an inclination, allows the stick to be kept more or less centered as soon as the desired inclination is achieved, thus improving pilot comfort. Furthermore, the ability to be able to meter the angular speed accurately is appreciable during large-amplitude dynamic maneuvers.
However, it is also known that control of the xe2x80x9ctrimxe2x80x9d type (using trim commands), whereby actuation of the control (in the example being considered, moving the stick sideways) directly brings about a proportional rotation (in the example being considered, a proportional inclination in terms of roll) of the helicopter, is better suited for certain phases of flight than the aforementioned speed control.
In particular:
on cruising flight on instruments, in poor visibility, control of the trim type makes it possible, when pressure on the stick is released on completion of a rolling maneuver, to return automatically to horizontal trim, which gives the pilot a great feeling of security. Conversely, maintaining constant inclination in order to effect a continuous turn, requires lateral pressure to be kept on the stick, and this in return gives the pilot tactile feedback regarding the inclination and allows him to pay a little less attention to the artificial horizon; and
for small corrections in heading which consist in banking then straightening out, trim control is intrinsically easier to manage because it requires only a pulse action (impulse) on the stick rather than alternating movements as are necessary for speed control. For precision tasks, such as following an ILS line of approach, this characteristic in particular makes it possible to obtain a more precise path.
However, whatever the control axis considered and whatever the type of aircraft used, it is not possible for the two types of control (control by trim and control by speed) to be employed simultaneously or even combined. In consequence, whichever of these types of control is being used, there are always phases of flight for which the type of control used is hardly appropriate.
The present invention relates to a flight control device (mechanical or electrical) for an aircraft, particularly a helicopter, that makes it possible to overcome these drawbacks.
To this end, according to the invention, said flight control device of the aforementioned type is noteworthy in that it additionally comprises:
at least one sensor for determining a second value which represents the control executed by the aircraft, with respect to said control axis; and
second means associated with said first means so as to determine, as commands to be applied to said actuating means:
as long as said second value is below or equal to a reference value, a first trim command that is proportional to said first value, said first value being equal to a limit value when said second value is equal to said reference value; and
when said second value is higher than said reference value, a second trim command which is proportional to said limit value and a speed command that is proportional to the difference between said first value and said limit value, that is to say proportional to the additional actuation with respect to the actuation that represents said limit value, that allows the aircraft to be brought to the aforementioned reference value.
Thus, by virtue of the invention:
actuation of the control (for example moving the control stick sideways) generates an aircraft trim command (for example an inclination in terms of roll) that is proportional to this actuation, as far as said reference value;
beyond this value (the aforementioned roll inclination threshold, for example), the additional actuation of the control gives rise to a speed command (for example an angular roll rate) proportional to this additional actuation,
which makes it possible to combine the two types of control (trim and speed) in such a way that each control is active in those areas of flight in which it is the most effective.
In particular, trim control is thus active for small corrections, for example of heading, and speed control is thus active for large-amplitude maneuvers.
In consequence, the device according to the invention makes it possible to combine the advantages of the two types of control. In addition to the aforementioned phases of flight, the invention is also advantageous in tactical flight close to the ground, particularly in poor visibility or by night.
As mentioned previously, the device according to the invention is particularly appropriate to control with respect to the roll axis. However, it may of course also be used (in addition or as an alternative) for control with respect to the pitch and yaw control axes.
In addition, in a particular embodiment, said device comprises controls, actuating means, sensors and first and second means for controlling the aircraft with respect to each of the control axesxe2x80x94roll, pitch and yawxe2x80x94of the aircraft.
Furthermore, according to the invention, said reference value of the aircraft in terms of roll is adjustable in flight, either by action of the pilot or automatically from information that determines the flight scenario.
The single figure of the drawing allows a good understanding of how the invention may be achieved. This figure is the block diagram of a flight controls device according to the invention.